91900991 has 8 divisors (see below), whose sum is σ = 113109024. Its totient is φ = 72712800.

The previous prime is 91900981. The next prime is 91900999. The reversal of 91900991 is 19900919.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 91900991 - 2¹⁰ = 91899967 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (91900999) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 504860 + ... + 505041.

It is an arithmetic number, because the mean of its divisors is an integer number (14138628).

Almost surely, 2^91900991 is an apocalyptic number.

91900991 is a gapful number since it is divisible by the number (91) formed by its first and last digit.

91900991 is a deficient number, since it is larger than the sum of its proper divisors (21208033).

91900991 is a wasteful number, since it uses less digits than its factorization.

91900991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1009921.

The product of its (nonzero) digits is 6561, while the sum is 38.

The square root of 91900991 is about 9586.5004563709. The cubic root of 91900991 is about 451.2737426600.

The spelling of 91900991 in words is "ninety-one million, nine hundred thousand, nine hundred ninety-one".